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  Illumination devices comprising white light emitting diodes and diode arrays and method and apparatus for making themUSPTO Application #: 20050224830Title: Illumination devices comprising white light emitting diodes and diode arrays and method and apparatus for making them Abstract: In accordance with the invention, an illumination device comprises a substrate having a surface and a cavity in the surface. At least one light emitting diode (“LED”) is mounted within the cavity, and a monolayer comprising phosphor particles overlies the LED. The phosphor monolayer is adhered to the LED by a monolayer of transparent adhesive material. An optional optical thick layer of transparent material overlies the phosphor monolayer to encapsulate the LED and optionally to form a lens. Methods and apparatus for efficiently making the devices are disclosed. (end of abstract) Agent: Docket Administrator Lowenstein Sandler PC - Roseland, NJ, US Inventors: Greg E. Blonder, Edmar M. Amaya USPTO Applicaton #: 20050224830 - Class: 257100000 (USPTO) Related Patent Categories: Active Solid-state Devices (e.g., Transistors, Solid-state Diodes), Incoherent Light Emitter Structure, Encapsulated The Patent Description & Claims data below is from USPTO Patent Application 20050224830. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] This invention relates to the illumination devices comprising white light emitting diodes ("white LEDs"). BACKGROUND OF THE INVENTION [0002] White LEDs are important in a wide variety of direct and indirect illumination applications. A white LED typically comprises a blue or ultraviolet LED whose emitted light is passed through a phosphor that converts the emitted light to white light. Such LEDs individually or in arrays can be used for room and space illumination, vehicle headlights, signs, and indicators. The emission spectra and color temperature of white LEDs is closer to sunlight than many forms of conventional lighting. [0003] Unfortunately, it is difficult to efficiently make white LEDs enough to compete with conventional light sources. One source of inefficiency is coating the LED with the optimal thickness of phosphor. There should be sufficient phosphor to convert the emitted light but not so much as to block or absorb the white light output. Further details concerning the structure and operation of white LEDs may be found, for example, in U.S. Pat. Nos. 6,576,930; 6,608,332 and 6,614,179 which are incorporated herein by reference. [0004] One approach to coating is to dispose the LEDs on a substrate, to dispense a thick transparent resin layer over the LEDs, and to apply over the transparent layer, a thin layer of resin containing phosphor particles. Ideally the resins dry to form a lens and an outer uniform phosphor layer around the diode. See, for example, U.S. Pat. No. 5,959,316. [0005] There are, however, two problems with this approach. First, the uniformity of the phosphor coating is dependent on the shape of the transparent layer which, in turn, is difficult to control, especially when the resin is dispensed and dried over a wire bonded array. Second, the presence of the intervening transparent layer separates the LED from the phosphor, causing an undesirable broadening of the effective optical area. [0006] In an attempt to overcome some of these problems, efforts were made to electrophoretically coat the LED with a uniform coating of phosphor. See U.S. Pat. No. 6,576,488. However this approach requires selectively masking some portions of the LED structure with conductive material (where phosphor is to be deposited) and other portions with dielectric material. The multiple masking and coating steps add substantially to the time and cost of fabrication. [0007] Accordingly there remains a need for improved white LEDs and LED arrays and for an improved method of fabricating them. SUMMARY OF THE INVENTION [0008] In accordance with the invention, an illumination device comprises a substrate having a surface and a cavity in the surface. At least one light emitting diode ("LED") is mounted within the cavity, and a monolayer comprising phosphor particles overlies the LED. The phosphor monolayer is adhered to the LED by a monolayer of transparent adhesive material. An optical thick layer of transparent material overlies the phosphor monolayer to encapsulate the LED and optionally to form a lens. [0009] The white LED or LED array can advantageously be fabricated by providing a substrate including one or more LEDs, applying a thin layer of tacky adhesive over the LEDs and applying a thin layer comprising particles of phosphor over the adhesive. The particles adhere to the tacky adhesive in a substantially uniform layer of self-limiting thickness. They selectively adhere where the tacky material is exposed. Advantageously, the thickness of adhesive and particle size are chosen to provide monolayers of desired thickness. Advantageous apparatus for practicing this method is described. BRIEF DESCRIPTION OF THE DRAWINGS [0010] The advantages, nature and various additional features of the invention will appear more fully upon consideration of the illustrative embodiments now to be described in detail in connection with the accompanying drawings. In the drawings: [0011] FIG. 1 is a schematic cross sectional view of a typical single LED packaged in accordance with the invention; [0012] FIG. 2 is a schematic cross sectional view of a typical array of LEDs packaged in accordance with the invention; [0013] FIG. 3 is a flow chart showing the steps in fabricating a white LED or LED array in accordance with the invention; and [0014] FIG. 4 is a schematic representation of a coating apparatus to facilitate coating the LEDs with phosphor particles. [0015] It is to be understood that these drawings are for purposes of illustrating the concepts of the invention and are not to scale. DETAILED DESCRIPTION [0016] Referring to the drawings, FIG. 1 is a schematic cross section of an exemplary white light emitting diode ("white LED") package assembly 100 for creating white light using a LED 101 and a fluorescent converting phosphor particle layer 102. The LED die 101 is placed on and advantageously wirebonded to the surface of a thermally conductive substrate 103 (preferably ceramic) inside a cavity 104. An optical adhesive monolayer 105 is placed on top of the LED body 101 and phosphor particles 106 forming layer 102 are adhered on top of the body. Also shown is an optional encapsulation dome lens 107 encapsulating the coated LED within the cavity 104. The package assembly 100 is composed of substrate 103, a highly reflective layer 108, usually silver, overlying the substrate and a conductive die attach material 109. LED body 102 is typically a nitride LED emitting blue or UV light, and can be connected using a wirebond 110. LED body 101 can have both P and N terminals on the top surface of the LED, in which case two wirebonds 110 will be attached from the top; or it can have both terminals on the bottom surface, using solder-bumping for attachment. [0017] In fabricating the assembly 100, LED body 101 is advantageously covered with a first sticky transparent material 105. The transparent material 105 can be covered with a single layer 102 comprising phosphor particles 106. Once deposited, the particles 106 can create a closed packed structured layer 102 film on top of sticky optical material 105. Ceramic cavity 104 can optionally then be sealed with a second transparent material 107 that advantageously forms a dome or lens in order to minimize total internal reflection ("TIR"). [0018] FIG. 2 illustrates a multiple LED array assembly 200 in which several LEDs 201, are placed inside a ceramic cavity 202 similar to the cavity 104 described above. Advantageously, multiple LEDs 201 can be attached on top of a highly conductive substrate 203, as by conductive epoxy 204. A transparent adhesive monolayer 205 is placed on top of the multiple LED bodies 201 and a layer 206 of phosphor particles 207 is adhered overlying and over the sides of the bodies 201. In fabrication, all LEDs 201 can simultaneously be coated with the first tacky transparent material 205. The particles 207 of the phosphor layer coating can attach to the tacky layer 205 creating a closed packed dense film layer 206. Then assembly 200 comprising wirebonded LEDs 201 can then optionally be sealed as by covering with a second transparent material 209 that can optionally create a dome or lens. The lens minimizes TIR. [0019] Substrate 203 can be metal, ceramic, multilayer printed wire board, LTCC, HTCC or other suitable thermal conductor. The substrate advantageously includes a heat sink. It can be electrically insulating or electrically conducting. Substrate 203 advantageously comprises a highly thermally conductive metal such as copper, tungsten or molybdenum and/or a highly thermally conductive ceramic such as aluminum nitride (ALN), silicon carbide (SiC) or aluminum oxide (Al.sub.2O.sub.3). In a preferred embodiment it can be nickel-plated copper molybdenum copper clad. Metal powder mixtures such as molybdenum copper, can be used in order to match the thermal expansion coefficient of the LED dies. Continue reading... Full patent description for Illumination devices comprising white light emitting diodes and diode arrays and method and apparatus for making them Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Illumination devices comprising white light emitting diodes and diode arrays and method and apparatus for making them patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. 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